Firstly the prices defied logic because people were paying 135 pumpkin to get 1000 titanium ore, which helped kill a golem that returned 40 pumpkins. So it is illogical to kill the golem if you can get far more pumpkins on the TO.
Players will set an ever increasing price if the demand is high and will obviously start dropping it rapidly if the demand is low, BB issues no guidance on anything from the prices of loot spots to the price of coal. In fact loot spots would be a good example you try selling an over priced loot spot in trade you soon get shouted down by a number of people telling you the real price and who set that price, the players did.